If I read your post right -- the way your insurance works is:
I'm a home buyer. I think the housing market is frothy right now, but I want to buy a home anyway. So I can use your insurance to protect myself in the event the value of my house decreases in the future.
Your company is directly responsible for the first 20% decline. After that, other companies are responsible for the rest. And even if you go out of business, I'm still covered by those other companies.
Firstly, is that correct?
Secondly, if so -- what happens if you go out of business and my house goes down exactly 20%? I assume that means I have no coverage.
Thirdly, who's insuring the houses after a 20% decline? And why should I have any reason to believe they'd still be in business if the market collapses 20%+? The last time that happened, almost every insurance company and investment bank went out of business.
Finally, how much does this cost as a percentage of the house's current value yearly? Roughly...
It's an interesting idea. Despite the fact that most home buyers anticipate house price appreciation to underperform historical averages (and a lot of buyers actually think prices will go down) -- a lot of houses are being bought. I think a lot of those people would want an option like this.